1. Field of the Invention
The invention relates to a variable-frequency microwave generator with a coaxial arrangement of a capacitive resonator and antenna for, in each case, a brief emission of a high-energy spectrum of damped sinusoidal oscillations during the discharge of the capacitor between the outer and inner electrodes of the resonator.
2. Discussion of the Prior Art
A generator of the above-mentioned type is described in DE 1 01 51 565 B4 as a mechanically tuneable resonant system, applied to a microwave generator of the type, which is explained functionally and in design terms in more detail in DE 1 03 13 286 B3 with reference to DE 1 01 51 565 B4. According to these documents, the capacitance, which is charged to a high voltage, between an inner electrode, which is in the form of a bottle, and a hollow-cylindrical outer electrode, which coaxially surrounds it, in an electromechanical resonator is discharged via a spark gap in front of the base of the inner electrode within a tubular surrounding housing that provides breakdown-resistant isolation. This leads to a rapidly rising and then severely oscillating current flow as well via an antenna, which is concentrically adjacent to the bottle, neck and widens in the form of a funnel for impedance matching. The discharge-current pulse with a typical duration of only a few nanoseconds leads to broadband emission of a microwave spectrum in the range from about 200 to 400 MHz, with such a high energy density that radio links that are formed in the relatively close vicinity can at least be adversely affected, and electronic circuits with physical structures matched to the resonance condition may in particular be subject to interference on the input side, or may even be destroyed.
In the case of a generator of this generic type, a variable-length electrical conductor is provided in the discharge current path upstream of the outer electrode for geometric resonance matching of the mid-wavelength of the emitted spectrum to the dimensions of said circuits. The spindle guide described there for axial movement of a short-circuiting link for adjustment of the length of the discharge current path admittedly allows continuous variation of the median frequency in the emitted spectrum, but requires a comparatively large and largely unused physical space, and is also mechanically quite complex. On the other hand, in practical use, there is normally no need at all for such frequency shifting; temporary displacement of the median frequency is frequently sufficient to observe the effect of instantaneous resonance matching in a specific constellation at the receiver end.
Against the background of this knowledge, the present invention is based on the technical problem of being able to at least temporarily, deliberately and effectively influence the emission frequency of a microwave generator of this generic type by means whose design is considerably less complex.